<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>javascript</title>
  <style>
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box
    }
    body {
      font-size: 14px;
      padding: 20px;
    }
    ul li {
      line-height: 30px;
    }
  </style>
</head>
<body>
  <ul>
    <li></li>
  </ul>
</body>
<script>
  function test() {
    let [a, b] = [1, 2];
    return {
      showName () {
        return a + b;
      },
      delVal () {
        [a , b] = [null, null];
      }
    }
  }
  var t = test();
  t.delVal();
  console.dir(t)
  console.log(t.showName())
  console.log(null + null);
</script>
</html>